Here's a small list of almost duplicate translation strings. It also contains some cases where gettext's plural could be used.

include/views/configuration.hostgroups.list.php:31 – (Only Super Admins can create group)
include/views/configuration.host.edit.php:193 include/views/configuration.template.edit.php:140 – (Only superadmins can create group)

include/classes/import/CXmlImport18.php:632 – Cannot add image.
adm.images.php:52 – Cannot add image

api/classes/CMaintenance.php:441 – You do not have permission to perform this operation
CAlert.php:504 api/classes/CApplication.php:825 api/classes/CApplication.php:836 ... – You do not have permission to perform this operation.

include/users.inc.php:98 include/users.inc.php:109 include/users.inc.php:144 – User cannot change status of himself.
api/classes/CUserGroup.php:421 api/classes/CUserGroup.php:532 – User cannot change status of himself

include/classes/import/CConfigurationImport.php:816 include/classes/import/CConfigurationImport.php:893 – No permission for Graph "%1$s".
include/classes/import/CXmlImport18.php:1567 – No permission for graph "%1$s".

include/views/configuration.item.edit.php:127 include/views/configuration.item.massupdate.php:77 include/views/js/configuration.item.edit.js.php:7 – No interface found
api/classes/CItemGeneral.php:229 – No interface found.

Plural:

host_discovery.php:250 --Cannot delete discovery rules
api/classes/CDiscoveryRule.php:624 discoveryconf.php:135 host_discovery.php:166 – Cannot delete discovery rule

adm.macros.php:147 – Cannot update macros
adm.macros.php:93 – Cannot update macro.

Typo:

"Unable to uploade file because "file_uploads" is disabled." – include/classes/helpers/CUploadFile.php:58

Possible simplifications:

include/page_footer.php:98 – Zabbix %s Copyright %s-%s by Zabbix SIA
include/views/general.login.php:47 – Zabbix %s Copyright 2001-2012 by Zabbix SIA

Why would I want to translate "Opera" or "Internet Exploder"?